The present invention relates to viscous clutches.
Viscous clutches are used in a wide variety of automotive fan drive applications, among other uses. These clutches employ relatively thick silicon oil (generally called shear fluid or viscous fluid) for the selective transmission of torque between two rotating components. It is possible to engage or disengage the clutch by selectively allowing the oil into and out of a working area of the clutch located between input and output members (e.g., between an input rotor and an output housing). A valve is used to control the flow of the oil in the working area between the input and the output. Recent clutch designs have been employed that allow the oil to be stored in the rotating input portion of the clutch while the clutch is disengaged, in order to keep kinetic energy available to the oil to allow rapid engagement of the clutch from the off condition. This also allows the clutch have a very low output speed (e.g., fan speed) while in the off position. It has also become common for the clutch to be controlled electrically. This has been done to increase the controllability of the clutch, and to also have the clutch capable of responding to multiple cooling needs in a vehicle. Some of the possible cooling needs are coolant temperature, intake air temperature, air conditioning pressure, and oil temperature.
Viscous clutches have been used in the past as a separate device installed on a rotating pulley on the engine front. Rotational inputs to the clutch have been traditionally been engine crankshafts and water pumps. During the past decade, cooling requirements have been increasing as a result of increasingly stringent engine emission reduction requirements. During this time, the use of a belted pulley has become a more common method of providing an input to the fan clutch, with the belted pulley (synonymously called a sheave) capable of increasing the fan speed in order to obtain more cooling air flow for a vehicle's heat exchanger(s). The belted drive is desirable due to its simplicity, low cost and ease of obtaining the desired speed. Due to the rotational input to the fan clutch being separated from the water pump or crankshaft, it is possible for the cooling system engineer to choose the exact fan speed required to provide the necessary and desired cooling for a given application.
In a typical belted fan clutch arrangement, a drive hub assembly is mounted on the engine face. The drive hub consists of a pulley that is rotatably mounted on stationary journal bracket, with a bearing providing the rotational capability between the journal bracket and the pulley. FIG. 1 illustrates a prior art viscous clutch 10 mounted to a drive hub assembly 12. As can be seen in FIG. 1, the pulley and hub assembly 12 are a separate system, and the clutch 10 is mounted to a shaft 14 secured to the pulley 16, which in turn is rotatably mounted on a stationary journal bracket 18 by bearing 20. The clutch 10 is configured as described in U.S. Patent Application Pub. Nos. 2009/0084650, 2009/0101463 and 2010/0140040. The fan (not shown) can be mounted on either the rear side or the front side of the viscous clutch 10 shown in FIG. 1. Example air flow for the system shown in FIG. 1 is from the right side to the left side of the drawing, though could have a different orientation in further embodiments. An electrical interface 22 is resident between the clutch 10 and the pulley 16 on the engine side of a fan (not shown) attached to the clutch 10, downstream in the path of the air, so that the electrical interface 22 cannot be drawn into the fan. Electrical power is delivered to the clutch 10 by means of an electromagnet coil 24 that is rotationally fixed. Magnetic flux from the stationary electromagnet coil 24 can be transmitted to rotating components of the clutch 10 without any wear components (i.e., without slip rings, brushes, or the like). Because the electromagnet coil 24 is stationary and the input shaft 14 for the clutch 10 rotates, the coil 24 must be mounted on a bearing 26. Typically, the bearing 26 is a single row deep groove ball bearing which has been chosen to minimize its width and cost. The use of a single row bearing also necessitates great care in the attachment of the electrical interface 22 to the engine. Any side loading on the wires of the electrical interface 22 can result in shortened bearing life or wire failures. The use of the external electromagnet coil 24 necessitates getting the magnetic flux from the outside of the clutch 10 to the inside where a control valve is used to control the flow of oil in the clutch 10 to provide for desired selective engagement.
The present inventors have discovered a way to combine a drive hub assembly with a viscous clutch in order to provide a high value package for cooling system designers. According to the present invention, it is possible to eliminate components and improve the function of the drive. Accordingly, the present invention provides an alternative viscous clutch design to those of the prior art.